Aug 242015


On this date in 2006 the International Astronomical Union (IAU) redefined the term “planet” such that Pluto is now considered a dwarf planet and not a planet. The definition of “planet” set in 2006 states that, in the Solar System, a planet is a celestial body which:

is in orbit around the Sun,

has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and

has “cleared the neighborhood” around its orbit (i.e. there is nothing else in its orbit).

A non-satellite body fulfilling only the first two of these criteria is classified as a “dwarf planet.” According to the IAU, “planets and dwarf planets are two distinct classes of objects”. A non-satellite body fulfilling only the first criterion is termed a “small Solar System body” (SSSB). Initial drafts included dwarf planets as a subcategory of planets, but because this language could potentially have led to the inclusion of several dozen objects classified as planets it was eventually dropped. The definition was a controversial one and has drawn both support and criticism from different astronomers, but has remained in use.

Here’s an Euler diagram of all the Solar bodies (click to enlarge):


According to current definition, there are eight planets in the Solar System. The definition distinguishes planets from smaller bodies and is not useful outside the Solar System, where smaller bodies cannot be found yet. Extrasolar planets, or exoplanets, are covered separately under a complementary 2003 draft guideline for the definition of planets, which distinguishes them from dwarf stars, which are larger.

Before the discoveries of the early 21st century, astronomers had no real need for a formal definition for planets. With the discovery of Pluto in 1930, astronomers considered the Solar System to have nine planets, along with thousands of smaller bodies such as asteroids and comets. Pluto was thought to be larger than Mercury.


In 1978, the discovery of Pluto’s moon Charon radically changed this picture. By measuring Charon’s orbital period, astronomers could accurately calculate Pluto’s mass for the first time, which they found to be much smaller than expected. Pluto’s mass was calculated to be roughly one twenty-fifth of Mercury’s, making it by far the smallest planet, smaller even than the Earth’s Moon, although still over ten times as massive as the largest asteroid, Ceres.

In the 1990s, astronomers began finding other objects at least as far away as Pluto, now known as Kuiper Belt objects, or KBOs. Many of these shared some of Pluto’s key orbital characteristics and are now called plutinos. Pluto came to be seen as the largest member of a new class of objects, and some astronomers stopped referring to Pluto as a planet. Pluto’s eccentric and inclined orbit, while very unusual for a planet in the Solar System, fits in well with the other KBOs. New York City’s newly renovated Hayden Planetarium did not include Pluto in its exhibit of the planets when it reopened as the Rose Center for Earth and Space in 2000.


Starting in 2000, with the discovery of at least three bodies (Quaoar, Sedna, and Eris) all comparable to Pluto in terms of size and orbit, it became clear that either they all had to be called planets or Pluto would have to be reclassified. Astronomers also knew that more objects as large as Pluto would be discovered, and the number of “planets” would start growing quickly if something were not done. They were also concerned about the classification of planets in other planetary systems. In 2006, the matter came to a head with the first measurement of the size of 2003 UB313. That measurement had shown Eris (as it was believed to be until the ‘New Horizons’ mission to Pluto) to appear to be slightly larger than Pluto, and so was thought to be equally deserving of the status of planet at the time.


The process of new discoveries spurring a contentious refinement of Pluto’s classification echoed a debate in the 19th century that began with the discovery of Ceres on January 1, 1801. Astronomers immediately declared the tiny object to be the “missing planet” between Mars and Jupiter. Within four years, however, the discovery of two more objects with comparable sizes and orbits had cast doubt on this new thinking. By 1851, the number of “planets” had grown to 23, and it was clear that hundreds more would eventually be discovered. Astronomers began cataloging them separately and began calling them “asteroids” instead of “planets”.

Because new planets are discovered infrequently, the IAU did not have any machinery for their definition and naming. After the discovery of Sedna, it set up a 19-member committee in 2005, with the British astronomer Iwan Williams in the chair, to consider the definition of a planet. It proposed three definitions that could be adopted:


a planet is a planet if enough people say it is;


a planet is an astral body large enough to form a sphere;


an object is a planet if it is large enough to cause all other objects to leave its orbit.

The decision had some cultural and social implications, affecting a variety of spheres such as textbook publishing, toy manufacture, and the like. Most educational books printed after 2006 use the new definition. The decision was important enough to prompt the editors of the 2007 edition of the World Book Encyclopedia to hold off printing until a final result had been reached. The new designation also has repercussions in the astrological world and finds mixed receptions, with differences of opinion as to whether to make any changes to astrological practice as a result of the redefinition. Most astrologers are a little vague about the outer planets anyway, since they were not part of old systems of astrology created before the invention of the telescope, and move so slowly through the constellations that nothing much changes because of them for a long time.

The verb “to pluto” (preterite and past participle: plutoed) was coined in the aftermath of the 2006 IAU decision. In January 2007, the American Dialect Society chose “plutoed” as its 2006 Word of the Year, defining “to pluto” as “to demote or devalue someone or something.” This is really a bit silly. Pluto was not “demoted.” It was reclassified for perfectly legitimate scientific reasons. Thinking of the reclassification as a demotion is strictly an emotional reaction based on a simplistic conception of the Solar System as taught in elementary school. There’s all kinds of junk whizzing around the sun (comets being my favorite). Giving a few bits of that junk a different name is nowhere near as important as marveling in the majesty of it all.


Pluto does not conjure up a swarm of ideas for a recipe du jour. However, in certain parts of Australia a variety of corn dog is known as a “pluto pup” so there we have it. Pluto pups are sometimes called “dagwood dogs” or “dippy dogs” but no one seems to know the origin of any of these names. I did a fairly diligent search for clues but came up empty. Since do one else seems to care, I won’t either.

Pluto pups can vary somewhat, but the basic idea is to mount a hot dog on a stick, coat it in batter, and deep fry it. Obviously you can create variants by altering the batter you choose, or using a different kind of sausage instead of a hot dog. Have at it. My choice would be for an egg batter and a chipolata (thin beef sausage). My basic batter recipe is here.

If using any sort of raw sausage in place of a hot dog, it’s best to cook it before battering and deep frying. Take your pick of methods to cook the sausage: shallow fry, grill, broil, or whatever. Fat German sausages can be used although they are a tad unwieldy. I boil them in beer and then grill them until browned all over.

I wouldn’t consider making these at home, except possibly for a children’s party.  For me this is strictly street food or carnie food. You can get something similar in China where hot dogs are a popular snack.  Dipping sauces vary from ketchup to oyster sauce and the like.  Your choice.